Sharif Digital Repository

The compounds with composition GdBa2Cu3-xV xO7-δ and x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.3 have been prepared by the solid-state reaction method. The XRD spectra indicate single-phase formation of the compounds. The transition temperature decreases considerably with vanadium concentration to Tc = 26.4 K for x = 0.3. The host sample is in the orthorhombic phase, but by increasing the V content the structure approaches the tetragonal phase, and for x = 0.3 the structure is nearly tetragonal. The normal state resistivity has been compared with 2D-VRH, 3D-VRH, and CG regimes, which shows that the 2D-VRH and CG are in better agreement for our samples. The localization length is calculated for the... 

TmBa2_xPrxCu3O7+δ and LuBa2_xPrxCu3O7+δ samples with 0.0 < x ≤ 1.0 have been prepared by a solid-state reaction technique. The occurrence of the orthorhombic to tetragonal phase transition, increasing of oxygen content with the increase of Pr doping, and the existence of solubility limit in both systems confirm the correct substitution of Pr at Ba sites. The solubility limit for Pr in the Lu-based samples is less than 0.7, which is less than x = 0.90 for the Tm-based samples. The Tc depression versus doping content in both systems shows that depression of superconductivity by Pr at Ba sites is mostly due to the hole-filling/localization effects. Also, in the Tm-based system, the... 

This paper presents the prediction of nonlinearities in the superconducting microstrip straight bends in microwave frequencies based on two different methods; FDTD simulation as a numerical approach, and nonlinear circuit modeling as an analytical method. In the FDTD method, the superconducting microstrip structures are simulated with London's equations. In the simulation, the penetration depth and normal conducting coefficient are considered as functions of current density of superconductor. To simulate the thin strip of superconductor, a non-uniform mesh has been used. For the nonlinear circuit modeling, we use distributed RLGC parameters for superconducting microstrip transmission lines.... 

We show that high-temperature superconductors can be used to build a terahertz superlens. These materials exhibit hyperbolic behavior at frequencies between their two plasma frequencies corresponding to electric fields parallel and perpendicular to their c-axis. Due to the large component of permittivity perpendicular to the c-axis, the resolution of the proposed lens is much below the diffraction limit (λ/1000). In this paper we demonstrate this lensing phenomenon with a simple slab of a high-temperature superconductor. © 2019 Optical Society of America  

We show that high-temperature superconductors can be used to build a terahertz superlens. These materials exhibit hyperbolic behavior at frequencies between their two plasma frequencies corresponding to electric fields parallel and perpendicular to their c-axis. Due to the large component of permittivity perpendicular to the c-axis, the resolution of the proposed lens is much below the diffraction limit (λ/1000). In this paper we demonstrate this lensing phenomenon with a simple slab of a high-temperature superconductor. © 2019 Optical Society of America  

After about two decades of intense research since the discovery of high-temperature superconductivity (HTSC) in cuprates, although many aspects of the physics and chemistry of these cuprate superconductors are now well understood, the underlying pairing mechanism remains elusive. Magnetism and superconductivity are usually thought as incompatible, but in number of special materials including HTSCs these two mutually excluding mechanisms are found to coexist. The presence in a system of superconductivity and magnetism, gives rise to a large number of interesting phenomenon. This article provides perspective on recent developments and their implications for our understanding of the interplay... 

The phase formation and the variation of the normal phonon frequencies of high temperature superconductors YBa2Cu3O7-δ and GdBa2Cu3O7-δ upon doping Tb and Ce for Y and Gd, respectively, have been investigated using XRD and Raman spectroscopy measurements. It is found that the increase of doping content causes the formation of impurity phases that can be detected in the XRD and Raman spectra, and results in the suppression of superconductivity. Moreover, analysis of the Raman peaks reveals that substitutions of Tb and Ce for Y and Gd in the parent structure are restricted to low concentrations in favor of impurity island formation. © 2008  

The bulk samples of GdBa2Cu3-xCrxO7-δ with x = 0-0.3 have been prepared by the conventional solid-state reaction method. Structural phases were determined by powder X-ray diffraction. The XRD and the unit cell parameters were obtained through Rietveld refinement of the XRD data. By increasing the doping, the c parameter decreases and the a parameter increases, and by the nearly fixed b parameter, the orthorhombic phase approaches to the tetragonal phase. The resistivity measurements show a strong effect of doping on suppression of Tc. At the first doping step of x = 0.05, Tc decreases abruptly to 57 K, but by increasing the doping, this rate slows down and becomes nearly linear for higher... 

Gd(Ba2-xPrx)Cu3O7+δ single phase polycrystalline samples with 0.0 ≤ x ≤ 1.0 were investigated for structural, electronic and flux dynamics properties. Two-dimensional variable range hopping (VRH) is the dominant conduction mechanism in the normal state of the system. Pr doping strongly localizes the carriers in normal state, and finally causes the suppression of superconductivity. The effect of Pr substitution in 123 structure of HTSC at R or Ba sites is to increase the pseudogap temperature Ts, although, Pr at Ba sites has a stronger effect on the increase of Ts and suppression of superconductivity. The magnetoresistance of the samples have been studied within thermally activated flux creep... 

Application of a fast hybrid transfer switch (HTS) as a suitable tool for protection of sensitive electrical loads against power quality problems has attracted much attentions these days. In this paper, methods for desired control of a HTS which consists of a fast fault-detection method and a suitable firing and transfer strategy are proposed. Simulation results of a HTS under various operating conditions for two types of medium-voltage electrical systems, i.e. grounded (star connection) and ungrounded (delta connection) systems, with respect to total transfer time are presented. The results show the capability of the HTS and the proposed control methods in fast transferring of sensitive...